Home Forums Hunting & Shooting Ask The Gunwriters Subsonic loads for a .300 WM

I was thinking about loading some up, when it was pointed out to me that loads under minimum have been known to produce pressure spikes.

While that's been widely reported, last time I checked, no one could reproduce this in a lab.

Also, we have a model for light loads in large cases: the 45-70, for one, where you can load WAY down from case capacity with smokeless powder.

So, is it a problem to produce such loads?

Loads have been known to spike and even blow up some guns with very slow burning powders with small charges, but with fast to medium burning powders and a filer, I use Dacron or those foam plugs from Jeffs Outfitters, you won't have any problems at all..I used to shoot them all the time, but have not for a number of years now. About the same as using lead bullets in your big game rifle.

I think I have the solution in Trail Boss powder.

Speer #12 shows SR 4759 in .300 Wby over a variety of bullet weights. Most are shown at 2000 fps. I've used this powder a lot in reduced loads and I've had no issues.

Trail Boss is meant to be shot in a specific PRESSURE range. If you drop down very far it is not appropriate (per Hodgdon).

Blue Dot seems to be a lot easier to work with, as it seems that so long as you stay below the high-end on pressure then you can go downward as far as you want. I think that large capacity magnums might be a little squirrly with really reduced loads so would be careful there.

Pressure spikes aren't the only problem with subsonic loads. Sometimes during load development you can stick one in the bore. There is a lot of info available on this if you read about the .300 Whisper.

I loaded some Trail Boss, 11 gr. It shot fine, not quite as quiet as I wanted, but about like a CB cap. Used 170 gr. flat point bullets.

I disagree about the use of Trail Boss, although you will obtain average results.

Here is where you need to be:

http://www.gmdr.com/lever/lowveldata.htm

On the left side under 300 Win Mag click on the 170gr FN data tab.
Most people use powders far too slow for sub sonic shooting and the have position problems which leads to large extreme spreads and "poor" accuracy.

Greg Mushials data is tested. safe and reliable.

Be sure to read the context pape at the top of the list of cartridges

I would look at using cast bullets and unique for such loads. Yes, you'll have to be careful as the charge weights will be well under 1/2 case full. But you should achieve decent accuracy, mild recoil and mild report.

The pressure spikes you are likely thinking of are referred to as Secondary Explosion Effect (SEE) you can find info via google. My understaning is that the primer and initial burn of powder push the bullet into the rifling, the bullet comes to a stop, the bore is obstructed, the powder finally gets going, and kablooey.

I've never read of a problem with small charges of faster powders, it's the reduced slow powders that cause the problems as the slower powders are tougher to get lit off when reduced.

And you're not going to get truly quiet unless you use a supressor. The only way I know to get quiet and decent performance sans supressor is a small case, like a 45 acp, small charge of fast powder, and a heavy for caliber cast bullet. The expansion ratio will be such that pressure will really drop by the time the bullet leaves the barrel. But with a large case and small bore, you need a can to quiet it down.

I have a silencer. Which is why I'm going subsonic. Not looking for much accuracy, just a kind of a hobby.

I can't imagine it getting any quieter than a CB cap...

Even with the can the problem seems to be the primer "snap."

With very fast powders you will find the accuracy and reasonable quiet you are looking for.
No need for gas checks, the gc bullets shoot fine without it. Shoot them unsized and tumble lubed and save yourself a lot of "fuss and muss."

Some powders are very position sensitive. Trying Accurate 9 in my 30-30, I had a large difference in MV with the powder at the front of the case vs. the rear. Other powders do not have this problem. TiteGroup and 5744 are two that I have tested that do not have this problem, so far as I can tell.

Hodgdon's instructions for Trail Boss are to mark a case with where the base of the bullet will be, fill the case to there, and weigh the powder. That is a safe maximum load. Multiply this weight by .7, and you have a safe minimum load. Since your case is "reasonably" full, you should not have the position sensitivity problem.

In my 30-30 it only takes 12 grains of Trail Boss to fill the case. A jar of TB is only 9 ounces, and that is all that will fit in the jar.

Brownell showed a huge increase in pressure variability below about 30 KPSI in the 30-06. The scary thing is that he was using 4064 or 3031 if I remember correctly. The SEE problem is well known with 4831, but I suspect it is not unique to really slow burning powders.

Brownell did some pretty interesting work in this area that does support the existence of SEE. He shows pressure traces that literally have sharp, tall spikes riding on them.

I'm not set up to cast .30 caliber bullets. And I don't know if the can is friendly toward them. The only bullet mould I have in 30 caliber is on an Ideal Tool from long ago. It's for a 30-30. A neat tool, the Ideal.

As for it sounding like a CB Cap, could be a little louder. It's been a while since I shot any, but that's what came to mind when I shot it. I shot them inside my house out an open door, and didn't need hearing protection.

On reduced charges in general, for old black powder loads, the given
to load them with smokeless powder, is to take the BP weight and use instead 29% of the BP load with 4198, which gives about the same velocity. With a 45-70, this amounts to about 21.7 of 4198, and doesn't come close to reaching 50% of the case capacity, but you don't hear them blowing up. Maybe case design has something to do with it.

Also, crimping bullets might be a thing to do to reduce the primer snap, if we're talking about the same thing. The bullets I'm using have a crimping groove so I might try that.

The silencer really shines with full-house loads. No, it doesn't make them silent, but sure makes them a LOT less noisy, and reduces recoil significantly. Get a lot of barrel heat after a few rounds.

Not nit picking but a Jar/jug is 9 ounces not 9 grains. I've got three jars coming from powder valley to do some subsonics in .223


Mike

LOL. Yes, you are right. Thanks for the catch.

I would suggest an email to Johan, who is the senior ballistician at Accurate powder co. He's been quite helpful to me recently in developing some reduced loads. I would think that AA5744 would be the answer to your problem. No filler needed with this powder!

Sorry I no longer have the link, but go to AA's site, and use the contact us link there.

That is useful info as I like to dink and plink around with my .30-30 and cast bullets. I don't see that on the Hodgdon website or the IMR website. Do you have a link to that information?

The Hodgdon site has Trail Boss loads for the 30-30 from 997 fps to 1195 fps.